1. Field of the Invention
The present invention relates to a schottky contact which comprises an epitaxial diamond layer.
2. Description of the Related Art
Currently, silicon (Si) is predominantly used as a semiconductor material. Si is used in semiconductor devices which constitute an integrated circuit such as a logic circuit or a memory. Among the semiconductor devices, a metal oxide semiconductor (MOS) field effect transistor which can be easily highly integrated is used as the memory, and a bipolar transistor is used as a logic operator device which is required to act at a high speed.
Further, Si is used in various electronic devices such as an analog IC. A compound semiconductor such as GaAs or InP is being developed for specified applications such as optical devices and ultra high speed ICs.
However, Si cannot be used at a temperature higher than 200.degree. C. and GaAs cannot be used at a temperature higher than 300.degree. C. A carrier concentration increases since Si is intrinsic at temperatures higher than 200.degree. C. due to its small band gap of 1.1 eV, and GaAs is also intrinsic at the temperature of not lower than 300.degree. C. due to its small band gap of 1.5 eV.
Integration of integrated circuits have recently increased more and more, with a corresponding higher tendency for the device to generate heat. Since the heat causes malfunctions of the circuits, a way of releasing the heat is sought.
To solve the above problems, it is proposed to prepare a semiconductor device with good thermal resistance and good heat release by utilizing a diamond (cf. Japanese Patent Kokai Publication Nos. 213126/1984 and 208821/1984). Since diamond has a large band gap of 5.5 eV, the temperature range which corresponds to the intrinsic range of the diamond does not include temperatures lower than 1400.degree. C. at which the diamond is thermally stable. The diamond has high chemical stability. Thus, the device made from the diamond can operate at an elevated temperature, with good environmental resistance. The diamond has a thermal conductivity of 20 [W/cm.K] which is 10 times larger than that of Si, and good ability to release heat. In addition, the diamond has a large carrier mobility (electron mobility: 2000 [cm.sup.2 /V.sec], hole mobility: 2100 [cm.sup.2 /V.sec] at 300K), a small dielectric constant (K=5.5), a large electrical field at breakdown (E.sub.B =5.times.10.sup.6 V/cm), etc. Thus, the diamond has the possibility to be used as a material for a device to act at a high frequency and large wattage.
The single crystal diamond layer which acts as an operating layer of the semiconductor device can be epitaxially grown on a single crystal diamond substrate by a vapor phase deposition method. Either of p- and n-type semiconductors can be prepared through the doping of suitable impurities. A schottky contact which is one of ways of preparing a device from the semiconductor can be formed by a combination of the p-type diamond and a metal such as gold (Au) or tungsten (W).
However, the epitaxial diamond layer has electrical properties which significantly vary with its crystallinity like other semiconductive materials. When the crystallinity is not good because of, for example, the presence of defects, a carrier mobility is small and the operation of the semiconductor device is disturbed by the defects.
The surface morphology of the diamond layer also has influences on the electrical properties. When the surface of the diamond layer on which the schottky contact is formed is rough, many interface levels are formed between the diamond layer and a schottky metal electrode formed thereon, and, as to schottky properties, a leakage current in the reverse direction is large or no rectification property is realized.